Radionuclide deposition control

ABSTRACT

The deposition of radionuclides manganese-54, cobalt-58 and cobalt-60 from liquid sodium coolant is controlled by providing surfaces of nickel or high nickel alloys to extract the radionuclides from the liquid sodium, and by providing surfaces of tungsten, molybdenum or tantalum to prevent or retard radionuclide deposition.

The invention was made in the course of, or under, a contract with theEnergy Research and Development Administration.

BACKGROUND OF INVENTION

The invention relates to the use of specific materials to control thedeposition or non-deposition of radionuclides of cobalt and manganesefrom liquid sodium.

The sodium coolant for sodium cooled fast breeder reactors becomes acarrier of radioactive isotopes which may be high temperature corrosionproducts, or neutron irradiation products, or the like from the variouscomponents that are in contact with the liquid sodium. The activityresulting from the corrosion product transport and subsequent depositionon primary heat transport system surfaces is a serious problem thatlimits access time for maintenance of system components such as pumps,pump shafts, intermediate heat exchangers, valves, flow and temperaturesensors, etc. This problem may be of a more serious nature, if, duringoperation of the liquid metal fast breeder reactor, fuel failure occursso that the problem is intensified due to possible fission productrelease.

The radionuclides that present the greatest problem include manganese-54(⁵⁴ Mn), cobalt-58 (⁵⁸ Co) and cobalt-60 (⁶⁰ Co). While otherradionuclides may also be present and may also limit access time formaintenance purposes, the present invention is directed to the abovecited specific radionuclides.

It would be desirable to eliminate or reduce the problem of radionuclideconcentration in areas where maintenance of system components isrequired and it would likewise be desirable to control the areas inwhich this radionuclide deposition takes place or does not take place.

SUMMARY OF INVENTION

In view of the above limitations and goals, it is an object of thisinvention to provide a process for controlling the deposition ornon-deposition of specific radionuclides from liquid sodium.

It is a further object of this invention to provide a process forchemically separating radionuclides manganese-54, cobalt-58 andcobalt-60 from a liquid coolant.

It is a further object of this invention to provide for the removal ofradionuclides from liquid sodium at various temperatures.

It is a further object of this invention to provide an apparatus thathas at least 75 percent efficiency in removing manganese-54 andcobalt-58 and cobalt-60 radionuclides from flowing molten sodium.

It is a further object of this invention to overcome prior artlimitations by providing surfaces onto which said radionuclides will notdeposit.

It is a further object of this invention to provide an apparatus thathas at least 75 percent efficiency in inhibiting or preventing thedeposition of manganese-54, cobalt-58 and cobalt-60 radionuclides fromflowing molten sodium.

It is a further object of this invention to provide a liquid sodiumcooled fast breeder reactor system wherein the sodium coolant systemcomponents do not have the radioactivity derived from manganese-54,cobalt-58 and cobalt-60 which would otherwise limit access time formaintenance of the system components.

It is a further object of this invention to provide a novel trapconfiguration for removing radionuclides from liquid sodium.

It is a further object of this invention to provide a novel traplocation for removing radionuclides from liquid reactor coolants.

Various other objects and advantages will appear from the followingdescription of this invention and the most novel features will beparticularly pointed out hereinafter in connection with the appendedclaims. It will be understood that various changes in the details,materials, and layout of the apparatus and process which are hereindescribed and illustrated in order to explain the nature of theinvention may be effected by those skilled in the art without departingfrom the scope of this invention.

The invention comprises controlling the deposition of radionuclidesmanganese-54, cobalt-58, and cobalt-60 from liquid reactor coolants suchas liquid sodium by positioning a high surface area material of nickelor a high nickel content alloy in a flow of sodium containingmanganese-54, cobalt-58 and cobalt-60 to effect deposition of theradionuclides on the materials, and subsequently separating theradionuclide loaded material from the sodium stream; and positioningcomponents where deposition is undesirable having surface areas made oftungsten, molybdenum or tantalum in those areas where the liquid sodiumflow is contacted. The high surface area material may be in the form ofa radionuclide trap comprising an elongated cylindrical core, a nickelsheet of from about 0.13 mm to 0.25 mm thickness having a plurality ofdiagonal grooves on a face thereof, said sheet of material being wrappedaround the elongated cylindrical core to form a plurality of layers ofthe sheet about the core. The diagonal grooves form long helicalpassageways for the passage of sodium therethrough and the deposition ofthe radionuclides on the trap material. The nickel material may besuitably disposed in a housing which may then be located in reactor fuelelement subassemblies adjacent to and immediately downstream of the fuelpins.

DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a flow sequence or sodium loop for the liquid metalcoolant.

FIG. 2 illustrates one geometry of a trap material that may be useful inthis invention.

FIG. 3 plots the manganese-54 activity along the length of a nuclidetrap made of nickel and along the length of a nuclide trap made ofcommercial AISI 1020 steel material.

FIG. 4 compares cobalt-60 activity distribution on traps of nickel andcommercial AISI 1020 steel.

FIG. 5 illustrates an alternate geometry of a radionuclide attractingmaterial useful for an apparatus of this invention.

FIG. 6 illustrates an embodiment that may be used for practicing thisinvention.

FIG. 7 plots the activity distribution of traps having the nickel trapmaterial configuration of FIG. 2 and traps having nickel trap materialconfiguration of FIG. 5.

DETAILED DESCRIPTION

As diagrammatically shown in FIG. 1, the liquid sodium coolant flowcircuit or loop 10 illustrates that liquid sodium is pumped by means ofpump 12 through an appropriate conduit 14 into the liquid sodium coolantsystem components such as intermediate heat exchanger 16, throughconduit 18 into other system components such as check valve 20, andthereafter through an appropriate conduit 22 past isolation valve 24into the reactor core fuel assembly duct 26 via conduit 28 and past fuelelements 30 to cool and remove heat from a plurality of fuel pins orelements 30 as known in the art. As the liquid sodium is pumped throughthe circuit, various radionuclides produced by the neutron irradiationare removed from the material that the liquid sodium contacts, and theseare carried into the heat transport system piping by the flowing sodiumand deposited at various locations which give rise to the problems notedin the Background of Invention.

For example, as the liquid sodium is pumped through the circuit, thevarious radionuclides may deposit on the pump, valves, etc., and onvarious other system components such that the radioactivity will buildup on each of these components and prevent or limit access time formaintenance.

While liquid sodium cooling systems are discussed herein, this inventionis easily applicable to systems using lithium coolants and other likematerials as coolants where these radionuclides are generated.

We have discovered that the problems or disadvantages of radionuclidedeposition in areas where such deposition is indesirable may be reducedor eliminated by disposing nickel or a high nickel alloy as a "getter"material in the path of the liquid sodium to effect contact of thesodium with the getter material having a high surface area, andsubsequent deposition of the various radionuclides on the surface of thegetter material. As noted in Table III, high nickel alloys, e.g. thosehaving greater than about 73 weight percent nickel, may be usedsuccessfully in this invention although at lower efficiency. Forconvenience, getter materials are referred to herein as nickelmaterials. This nickel material may be in the form of a trap 32schematically shown in FIG. 1, the sodium flow going by the fuelelements 30 into trap 32 and subsequently through a suitable conduit 35past isolation valve 37 through conduit 39 into pump 12 to again beginthe cycle.

It has been found that by disposing the nickel getter material as a trap32 at a location immediately downstream of and in close proximity to thefuel elements, i.e., in reactor fuel element subassemblies 33immediately above the fuel pins, the radionuclides may be effectivelyremoved, i.e., at least about 75% removal of the radionuclides maybeeffected. The location of the trap in this position removes theradionuclides before they can deposit in areas of the primary heattransport system that may require maintenance. Further, it is desirablethat the trap material have a high surface area and that there be aturbulent flow of the sodium through the trap.

We have found that the best getter material for manganese-54 removal isunalloyed nickel. Manganese-54 is the principal radionuclide of concernin the sodium flow circuit, since it is rapidly released and movesreadily in sodium to maintenance areas of the circuit. However, it hasbeen found that this nuclide is stable with respect to temperaturechange once deposited on the surface of one of the more active gettersas listed hereinbelow. For example, in direct comparison at hightemperature (about 593° C.) nickel takes up ten times as much activityas AISI 304 series stainless steel. Auger electron spectroscopy analysishas shown the manganese-54 activity to have penetrated more than 30,000angstrons (3 microns) below the nickel surface in 1,000 hours.

In short duration tests (about 100 hours), the cobalt nuclides appearedto move very slowly, either remaining in the source of the nuclides orredepositing almost immediately in the hot zone. Longer duration test(about 21,000 hours) show a slow movement of both cobalt-58 andcobalt-60 toward the colder (about 427° C.) areas of the loop. Presentgetter runs indicate that nickel is again the best potential gettermaterial for radioactive cobalt nuclides.

In the area of concern for this invention, the radionuclides of greatestconcern are the long-lived gamma emitters cobalt-58, cobalt-60 andmanganese-54 created by neutron interaction with the constituents ofstainless steel. Manganese-54 is leached from the hot stainless steelsurfaces by flowing sodium and redeposited in colder areas of the sodiumcircuit or preferentially in areas of high turbulence such as valveseats, flow meters, and locations where flow direction changesdrastically. The deposition is temperature dependent and increases asthe sodium is cooled.

The two cobalt nuclides are much less mobile in sodium, either stayingin place or being redeposited almost immediately in areas adjacent tothe radionuclide source.

We have further discovered that surfaces of these components that are incontact with the liquid sodium may be made from or have a coating oftantalum, tungsten or molybdenum, or combinations thereof, toeffectively reduce and inhibit the deposition of the radionuclides ontothese surfaces and thereby prevent or inhibit the increasedradioactivity from these radionuclides on these components. The coatingmay be applied through flame spraying or diffusion bonding to athickness of at least 25 microns. By using tungsten, tantalum ormolydbenum, the deposition of radioactive material is minimized in areasof the liquid sodium coolant circuit subject to contact maintenance,since tungsten, tantalum and molybdenum do not collect manganese-54,cobalt-58, cobalt-60 or cesium-137 at 500° C. and above.

Table I illustrates approximate comparative efficiency of variousmaterials for gettering or non-gettering of the specific nuclides at ahot (about 604° C.) and a cold (from about 204° to about 316° C.)temperature. These results are after exposure to a section of about 6.4mm outer diameter thin wall stainless steel tubing with 20 millicuriesof cobalt-60, manganese-54 and cesium-137 activity for a period of 2500hours at the specific temperature noted. Table II ranks the materials asgetters for the three radionuclides present in order of descreasingefficiency.

From the data of these tables, it may readily be seen that nickel is theoverall best getter for both manganese and cobalt isotopes in the hotand cold regions. By the same token, tantalum and molybdenum alsominimize the amount of deposition of the nuclides in both the hot andcold regions.

Table III illustrates the results of exposure of various alloys tomanganese-54 activity, expressed in counts per minute, on 12.7 mm by25.4 mm by 0.76 mm specimen, for two identical 1,000 hour runs tocompare a number of metals and alloys. Again it is noted that tantalumand tungsten are not affected in the hot zone by radioisotopedeposition, but the manganese-54 does deposit in the cold zone or in thecolder temperatures. From the Table it is also apparent that the highweight percent nickel alloys absorb or have radionuclide deposition thatis significantly less than the nickel element by itself, but is stillsignificantly greater than stainless steel structural materials.

                  Table I                                                         ______________________________________                                                  Hot (604° C.)                                                                      Cold (260° C.)                                   Material    60.sub.Co                                                                            54.sub.Mn                                                                             137.sub.Cs                                                                         60.sub.Co                                                                          54.sub.Mn                                                                           137.sub.Cs                         ______________________________________                                        Low Carbon Steel                                                                          140    29379   0    363  10665 981                                Ni Felt     4377   29073   0    1897 12728 0                                  Niobium     437    10239   0    400  3921  212                                Tantalum    202    156     0    42   601   147                                Cobalt      351    15114   0    509  1920  78                                 Molybdenum  123    101     7    41   1507  188                                Zirconium   210    990     23   22   3634  11322                              Titanium    247    7245    0    233  478   1902                               Stainless Steel                                                                           2168   5561    0    279  2301  65                                 Graphite    406    101     279  70   187   70782                              ______________________________________                                    

                                      Table II                                    __________________________________________________________________________    Hot .sup.54 Mn                                                                            Cold .sup.54 Mn                                                                        Cold .sup.137 Cs                                                                       Hot .sup.60 Co                                                                        Cold .sup.60 Co                         c/m         c/m      c/m      c/m     c/m                                     __________________________________________________________________________    1. Steel.sup.a                                                                        29379                                                                             Ni   12728                                                                             Graphite                                                                           70762                                                                             Ni   4377                                                                             Ni   1897                               2. Ni   29073                                                                             Steel.sup.a                                                                        10665                                                                             Zr   11322                                                                             SS.sup.b                                                                           2168                                                                             CO   509                                3. Co   15114                                                                             Zr   3634                                                                              Ti   1902                                                                              Nb   437                                                                              Nb   400                                4. Nb   10239                                                                             Nb   2921                                                                              Steel.sup.a                                                                        981 Graphite                                                                           406                                                                              Steel.sup.a                                                                        363                                5. SS.sup.b                                                                           5561                                                                              SS.sup.b                                                                           2301                                                                              Nb   212 Co   351                                                                              SS.sup.b                                                                           279                                6. Zr   990 Co   1920                                                                              Mo   188 Ti   247                                                                              Ti   233                                7. Ti   725 Mo   1507                                                                              Ta   147 Zr   210                                                                              Graphite                                                                           70                                 8. Ta   156 Ta   601 Co   78  Ta   202                                                                              Ta   42                                 9. Mo   101 Ti   478 SS.sup.b                                                                           65  Steel.sup.a                                                                        140                                                                              Mo   41                                  10.                                                                             Graphite                                                                           101 Graphite                                                                           187 Ni   0   Mo   123                                                                              Zr   22                                 __________________________________________________________________________     .sup. a AISI 1020 Steel                                                       .sup. b AISI 304 Stainless Steel                                         

                  Table III                                                       ______________________________________                                                         Hot Zone    Cold Zone                                        Material         (604° C.)                                                                          (454° C.)                                 ______________________________________                                        Ni               10339       7099                                             Inconel 750 (73% Ni)                                                                           4692        3771                                             Inconel 600 (76% Ni)                                                                           4215        3448                                             Inconel 625 (61% Ni)                                                                           1630        453                                              Inconel 718 (53% Ni)                                                                           1212        437                                              Nimonic PE-16 (43% Ni)                                                                         365         201                                              Mn/Co Alloy      1532        2018                                             Cobalt           1867        2165                                             Tantalum         6           528                                              Tungsten         4           1036                                             ______________________________________                                    

Scanning electronmicroscopy and auger electron spectroscopy (AES)analysis studies of nickel material that has been exposed for a periodof 1,000 hours have been conducted. The scanning electron microscopeshows a significant build-up of material on 1,000 hour nickel getterspecimens and a measurable manganese peak. AES analysis shows manganesein the same nickel specimen to have a relatively stable concentration toa depth of 800 angstroms and then slowly decreasing. At 12,000 angstromsthe concentration had decreased by 67 percent but manganese was stillpresent at 32,000 anstroms or 3.2 microns. The manganese concentrationof the surface was 31 times the manganese content of unexposed metal.The existence of excess manganese well below the nickel surfaceindicated that manganese is diffusing inward, vastly increasing theactivity takeup limit.

A nickel nuclide trap was fabricated to be positioned above the fuelzone in liquid metal fast breeder reactor fuel element subassemblies.This trap was made of 0.13 mm nickel sheet wound on a central 304stainless steel mandrel, the sheet forming a plurality of layers aboutsaid mandrel and the spacing between layers being provided by twistedpairs of 0.25 mm nickel wire appropriately connected, joined, or weldedto the nickel sheet at suitable intervals such as about 3.18 mmintervals. After exposure for 3,000 hours, the total loop activity wasestimated at 9.7×10⁷ disintegrations per minute for manganese-54, with8.5×10⁷ disintegrations per minute for manganese-54 located in the trap.Thus the trap was 88.6 percent effective for this radionuclide. Analysisof the trap indicated high activity at the inlet end of the trap forboth manganese-54 and cobalt-60 radionuclides. It has been found thatthere is maximum deposition at points of increased turbulence wheresodium leaves one segment or enters another, or under similiarconditions. The trap that gave this result had about 0.15 square meterof surface area and the sodium flow was directed in fifty five-3.18 mmby 0.5 mm deep parallel channels having an effective surface path lengthfor deposition of the radionuclides of about 0.48 m.

Another radionuclide trap was fabricated of 0.13 mm thick mild steel(AISI 1020) sheet, dimpled in a random pattern with indentations ofabout 0.51 mm depth, as indicated by indentations 40 on sheet 42 in FIG.2. This sheet, again rolled around a 9.6 mm diameter 460.8 mm lengthmandrel, provided a 0.14 square meter surface area trap 0.48 meter longwith a 0.51 mm channel between layers. After 3,000 hours at about 604°C., there was some manganese-54 deposition on the steel trap as well assome cobalt-60 deposition. The same trap configuration using nickel asthe sheet material resulted in much greater manganese-54 and cobaltradionuclide deposition.

FIG. 3 illustrates the activity in counts per minute of manganese-54along the length of several nuclide traps, such that a comparison of thegettering efficiency for nickel versus iron as a function of distancealong the trap may be achieved. The nickel nuclide trap is far moreefficient for manganese-54 than the steel trap.

From FIGS. 3 and 4, it is seen that the nickel trap is efficient atremoving radionuclides from flowing sodium and that nickel is farsuperior to mild steel as a trap material for manganese-54 and ismeasurably superior for cobalt-60.

FIG. 5 illustrates a sheet form that may provide an increased flowpathalong a minimal trap flow distance. The generally rectangular nickelsheet 50 may have a plurality of generally parallel, diagonally disposedgrooves 53 on a surface thereof spaced at suitable distance apart suchas about 0.25 mm deep and 6.35 mm apart. The interlayer spacing isprovide by the elongated, raised portion 54 on the opposite surface ofthe sheet, which portions 54 are coextensive with the parallel grooves,as the sheet is rolled about a mandrel 60, made of such as 304Lstainless steel, which forms the central core of nuclide trap 62 shownin FIG. 6. As the sheet 50 is rolled to make a trap segment, the groovesform a set of elongated arcuate parallel spiral paths or helical pathsor passageways for the sodium flow. These can be varied in length perunit trap length by varying the angle of the original diagonal grooves53. The trap therefore is the nickel sheet being convoluted about saidcenter support member in a spiral member effectively forming a pluralityof concentric sheet layers about the support member, the raised portions54 of the nickel sheet separating adjacent sheet layers and formingelongated arcuate helical passageways between the adjacent sheet layersand adjacent raised portions for passage of the coolant past theconvoluted nickel sheet in turbulent fashion through the passageways andeffect chemical deposition of the radionuclides on the sheet surfaces.After the sheet 50 is wound around the mandrel 60, it may be containedor housed within a suitable housing 64 of appropriate configuration, thehousing having a perforate bottom or screened end 66 to permit passageof the liquid sodium into and through the grooved 53 material. Housing64 likewise has an upper cover portion 68 having perforations 70 oropenings therethrough to permit outflow of the liquid sodium from thetrap while retaining the trap material in position. The housing mayconcentrically encase the convoluted sheet and the support member. Theend portions 66, 68 of the convoluted nickel sheet may be disposed inthe path of the liquid coolant stream to effect flow of the coolantlongitudinally of said convolutions, the housing retaining theconvoluted sheet disposed longitudinally in the liquid coolant stream,i.e., the axis of the center support member being parallel to the streamflow, and the end portions of the nickel sheet are disposed transverseto the liquid coolant stream flow.

FIG. 7 compares the results of a trap having getter materialconfiguration shown in FIG. 5 and one having the getter materialconfiguration shown in FIG. 2. The radioactivity profile indicates apeak at the upstream edge with a sharp decrease through the exit end ofthe trap, which is a favorable trap activity spread with peak activityat the leading edge and little activity or minimal activity at the exit.Quite obviously the manganese-54 trapping efficiency is much superiorfor the trap configuration of FIG. 6 which includes the trap material ofFIG. 2.

By employing the teaching of this invention, the radionuclidesmanganese-54, cobalt-58 and cobalt-60 may be effectively controlled inthe liquid sodium coolant loop such that undesired deposition of theseradionuclides is averted by incorporating the teachings of thisinvention in the sodium loop, that is by controlling where theradionuclides deposit by employing a nickel getter material as a trap inthe area of maximum radionuclide egress from the fuel system, andfurther by making the surfaces in contact with sodium upon which theradionuclides are not to be deposited as tungsten, molybdenum, ortantalum surfaces. These metals may be used to coat components uponwhich radionuclide deposition is undesirable, or the components may bemade of these metals. While 75% trap removal efficiencies forradionuclides manganese-54, cobalt-58 and cobalt-60 are referred toherein, efficiencies of 95% or better have been achieved in variousruns. Although AISI 1020 steel appeared sufficiently promising initiallyto warrant further testing, results obtained from exposure to flowingsodium proved that it was not satisfactorily accomplishing manganese-54removal.

What is claimed is:
 1. A method for controlling deposition ontocomponent surfaces of radionuclides manganese-54, cobalt-58 andcobalt-60 from a liquid metal stream containing said radionuclides andcontacting said component surfaces, comprising disposing a gettermaterial in said liquid metal stream with surfaces of said gettermaterial contacting said liquid metal stream to chemically getter saidradionuclides onto said getter material, wherein said getter materialcomprises at least 73 weight percent nickel.
 2. The method of claim 1wherein said liquid metal stream containing said radionuclides comprisesa nuclear reactor liquid metal coolant, and said radionuclides arereleased into said liquid metal stream from irradiation in said nuclearreactor.
 3. The method of claim 2 further including disposing in saidliquid metal stream a non-getter metal selected from the groupconsisting of tantalum, tungsten and molybdenum on said componentsurfaces that contact said liquid metal stream where deposition is notdesired to inhibit chemical deposition of said radionuclides.
 4. Themethod of claim 3 wherein said nuclear reactor liquid metal coolant isselected from the group consisting of sodium and lithium, said gettermaterial comprises essentially 100 weight percent nickel, and saidgetter material comprises a high surface area disposed immediatelydownstream of said radionuclide source and in a form to effect turbulentcontact of said stream with said getter material.
 5. The method of claim3 wherein said liquid metal stream comprises liquid sodium coolant for anuclear reactor, and including inhibiting deposition of saidradionuclides from said liquid molten sodium at at least about 75%efficiency, and, further, effecting deposition of said radionuclidesonto said getter material at at least about 75% efficiency.
 6. A methodfor inhibiting deposition of radionuclides manganese-54, cobalt-58, andcobalt-60 from a liquid metal stream onto component surfaces comprisingdisposing a non-getter material selected from the group consisting oftantalum, tungsten and molybdenum on said component surfaces contactingsaid liquid metal stream wherein said radionuclide deposition isundesired to inhibit deposition of said radionuclides from said streamonto said surface of said non-getter material.
 7. A system forpracticing the method of claim 1 for controlling deposition ofradionuclides manganese-54, cobalt-58, and cobalt-60 onto componentsurfaces in contact with a liquid metal containing said radionuclidescomprising a nuclear reactor liquid metal coolant circuit, a liquidmetal stream containing said radionuclides contained within said coolantcircuit, nuclear reactor heat transfer components housed within saidcoolant circuit and in contact with said liquid metal stream, a gettermade of a material comprising at least about 73 weight percent nickeldisposed in the path of said liquid metal stream within said coolantcircuit with surfaces of said getter material contacting said liquidmetal stream to effect chemical gettering of said radionuclides fromsaid liquid metal stream onto said getter material surfaces.
 8. Thesystem of claim 7 further including said nuclear heat transfer componentsurfaces being non-getter surfaces selected from the group consisting oftantalum, tungsten, and molybdenum to inhibit deposition of saidradionuclides onto said non-getter surfaces on said components.
 9. Thesystem of claim 7 wherein said liquid metal stream comprises a nuclearreactor liquid metal coolant selected from the group consisting ofsodium and lithium.
 10. The system of claim 9 wherein said liquid metalstream comprises a sodium metal coolant for a liquid metal fast breederreactor, said getter is made of nickel, and said radionuclides arereleased into the liquid metal stream from reactor irradiation.
 11. Thesystem of claim 8 wherein said getter material is nickel.
 12. The systemof claim 11 wherein said getter material for gettering saidradionuclides comprises a coating having a thickness of at least 25microns, and said non-gettering material comprises a coating having athickness of at least 25 microns.
 13. A system for practicing the methodof claim 6 for controlling deposition of radionuclides manganese-54,cobalt-58, and cobalt-60 onto component surfaces in contact with aliquid metal containing said radionuclides comprising a nuclear reactorliquid metal coolant circuit, said liquid metal disposed in said coolantcircuit, nuclear reactor heat transfer components housed within saidcoolant circuit and in contact with said liquid metal and non-gettersurfaces selected from the group consisting of tantalum, tungsten andmolybdenum on said reactor heat transfer components in contact with saidliquid metal wherein said deposition of said radionuclides is notdesired, to effect passage of said liquid metal past said componentshaving said non-getter surfaces and inhibit deposition of saidradionuclides on said non-getter surfaces.